The fallacy of coral bleaching and recovery?

serwobow

Well-Known Member
BRS Member
Almost every time I watch a program or read an article about coral bleaching in the ocean, it is described like this:

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"Warmer water temperatures can result in coral bleaching. When water is too warm, corals will expel the algae (zooxanthellae) living in their tissues causing the coral to turn completely white. This is called coral bleaching. When a coral bleaches, it is not dead. Corals can survive a bleaching event, but they are under more stress and are subject to mortality." (copied from NOAA . https://oceanservice.noaa.gov/facts/coral_bleach.html )


I think this is wrong. Corals cannot survive bleaching events. I have (sadly) killed well over a 100 different corals in my decade of reefing. I have never seen a completely white coral recover, or even attempt to recover.

In my experience, if a coral turns completely white, not only has it lost its zooxanthellae, but it has also lost its skin, and its polyps are also gone. In my book, a completely white coral is dead. Period.

I want to know what you guys think.

Have you ever seen a coral turn completely white, then recover?
 
I have had corals get white parts and the living part grows back over it... but never a recovery from completely white.
 
Had my Birds nest jump off its perch over night. Came down the next day to find my Yuma eating it as it landed on it. pulled it out and had several dead/white parts. within a couple weeks it started to regrow. have no had anything come back from full white out either
 
Sps can do it but it actually has to be bleached not with no skin on them. Bleached coral have lost its zooanthelia sp.
once in a while it can come back from it but not always
 
Sps can do it but it actually has to be bleached not with no skin on them. Bleached coral have lost its zooanthelia sp.
once in a while it can come back from it but not always

I think that you mean they need skin to be able to recover. I agree. I have never seen a completely white coral that still has skin. It is important, I think to make the distinction, so that people know what bleached, but recoverable, coral tissue looks like. To me, such a tissue is light brown or tan, and not ever completely white. The recoverable coral would be the "stressed" coral in the picture.
 
My monti cap has gotten pretty pale but wouldn’t quite call it white. Colored back up over the course of several months.

First pic is 11/09/2018

Second pic is 05/27/2019

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Sent from my iPhone using Tapatalk
 
When I get new corals, on many occasions I will see it "spit up brown goo", then bleach. Once it takes up the zooanthelia strain from the tank, it recovers.
 
I've had corals bleach and come back. Just had it happen in the past few months. The corals do not lose ALL color, they just dump their zooxanthellae and get pale. It happened in my tank at work due to two timers failing almost simultaneously and me not realizing it. Cooling fan stopped coming on and light was on 24/7. Corals don't like that. Tank also got warm and stayed warm until I realized the problem. Once corrected most corals recovered. One slow growing coral got an infection and completely died except for two tiny pieces I managed to cut off the edge before the biofilm of destruction reached them. It has taken weeks to months for the normal color to start to return to these corals. Small stressors at this point put them over the edge (passing parrot fish for instance, fortunately none in my tank).
 
I've been diving on bleached reefs in the Pacific as well. The SPS look really pretty...super pale and pastel colored (blues and pinks and purples), huge swaths like this (the water is usually super warm at this point too, ~85F, don't even need a wet suit) that you would normally never see. Unfortunately, if you know what's coming it's super depressing to see...cause usually it's the end. :(
 
I also have had corals become really pale, and then return to health over a couple months. It just seems that a misconception is widely propagated that completely bleached white coral tissue can recover. If it can, it must be very very rare.

What you describe with the pastels - I have also heard people talk about something similar happening on the GBR - the colors actually become brighter before bleaching. Is there a parallel in reef tanks to that phenomenon?
 
I have seen a Wild sps colony Dong got in and it was all white (Millipora I think). Not sure if it recovered.. that was over a year ago. @dz6t ?
 
Almost every time I watch a program or read an article about coral bleaching in the ocean, it is described like this:

View attachment 127416


"Warmer water temperatures can result in coral bleaching. When water is too warm, corals will expel the algae (zooxanthellae) living in their tissues causing the coral to turn completely white. This is called coral bleaching. When a coral bleaches, it is not dead. Corals can survive a bleaching event, but they are under more stress and are subject to mortality." (copied from NOAA . https://oceanservice.noaa.gov/facts/coral_bleach.html )


I think this is wrong. Corals cannot survive bleaching events. I have (sadly) killed well over a 100 different corals in my decade of reefing. I have never seen a completely white coral recover, or even attempt to recover.

In my experience, if a coral turns completely white, not only has it lost its zooxanthellae, but it has also lost its skin, and its polyps are also gone. In my book, a completely white coral is dead. Period.

I want to know what you guys think.

Have you ever seen a coral turn completely white, then recover?

This is not wrong.

The distinction you are missing is the difference between a bleached coral and a dead coral. A bleached coral has expelled the zooxanthellae and has a white appearance but still has living tissue. It can be repopulated with zooxanthellae when conditions permit. A dead coral also has a white appearance but no living tissue.

A bleached coral has a specific definition and is not just the colloquial use of the word "bleached" that means white.

Bleached corals can recover. Dead corals cannot.

If anecdotal evidence that bleached corals in our tanks do not recover is correct, it is likely because we don't have enough zooxanthellae or similar corals in our tanks to repopulate the bleached coral, unlike in the ocean.

It's not really disputed that corals can recover from bleaching. It happens all the time and is happening right now.
 
Yes as others have said, Bleaching and RTN/STN is not the same thing even though they both look similar, bleach white corals. In traditional bleaching, the tissue is all still there, it is just translucent (the actual natural state of corals) thus you can see the bleach white skeleton underneath, in RTN the tissue itself is gone leaving only the bleach white skeleton.
 
I looked at the papers recommended by Kelly's Reef, and I pasted a figure from one of them below, which shows what they considered bleached corals (which may have later recovered). To my eye, these are pale.

Some academic papers describe levels of bleaching, which have to do with the extent to which the symbionts are lost. From this way of defining bleaching, the pastel colored corals are also bleached to a degree, and perhaps any paling coral can be called bleached. These may recover, as many have observed.

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Rowan, R., Knowlton, N., Baker, A., & Jara, J. (1997). Landscape ecology of algal symbionts creates variation in episodes of coral bleaching. Nature, 388(6639), 265–269. http://doi.org/10.1038/40843
 
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